Phase-change-driven tuning of linear and nonlinear optical properties of Te/As2Se3 bilayer thin films for optoelectronic applications

Abstract

The present work reports the amorphous-crystalline phase transformation by interdiffusion of Te into the As2Se3 matrix with annealing at various temperatures (100, 150, and 200 °C). Te/As2Se3 bilayer thin films were prepared by electron beam evaporation under high vacuum conditions. The amorphous nature of As2Se3 thin film was confirmed from the X-ray diffraction study. The presence of small peaks in Te/As2Se3 thin film indicates the As4Te4 (monoclinic) and As2Se3 (monoclinic) phases, confirming the amorphous to crystalline phase transformation upon Te interdiffusion and subsequent annealing. The impact of Te top layer deposition on the vibrational modes were also observed from the Raman spectroscopy. The formation of Te agglomerates is confirmed from the morphological analysis which disappeared with further annealing. Furthermore, the water contact angle measurements have provided insight into surface interaction mechanisms of these materials. The linear and nonlinear optical properties were changed upon interdiffusion of Te as observed from UV–Visible spectroscopy. The increase in Eu indicated an increase in disorder hence the decrease in the bandgap. The 3rd order nonlinear susceptibility (χ3) and nonlinear refractive index (n2) increased with annealing. The tuning of linear and nonlinear optical properties by annealing can be used in various optoelectronic applications. Specifically, the phase transformation behaviour of Te/As2Se3 bilayer thin films enables their utilization in phase-change material-based optoelectronic devices.